Engine fuel may be pumped out of a fuel tank by a lift pump. The lift pump propels fuel towards a fuel rail before being injected by fuel injectors. A check valve may be included between the lift pump and the fuel rail to maintain fuel rail pressure and prevent fuel in the fuel rail from flowing back towards the lift pump. Operation of the lift pump is typically feedback controlled by an engine controller based on outputs from a pressure sensor coupled in the fuel rail. The controller attempts to maintain the pressure in the fuel rail to a desired pressure by adjusting an amount of electrical power supplied to the lift pump based on a difference, or error, between the desired fuel pressure and a measured fuel pressure obtained from the pressure sensor.
Thus, the lift pump replaces fuel lost to injection in the fuel rail. As fuel injection rates decrease therefore, the fuel resupply demands of the fuel rail correspondingly decrease, and the controller reduces the electrical power supplied to the lift pump. Consequently, the energy demands of the lift pump may be substantially proportional to fuel injection rates. In some examples, such as during engine idle and/or deceleration fuel shut-off (DFSO), the amount of electrical power supplied to the lift pump may drop sufficiently low, such that it may be more energy efficient to operate the lift pump in a low fuel flow mode. In the low fuel flow mode, the lift pump is not continuously powered nor powered via a duty cycled voltage as it would be with pulse width modulation (PWM). Instead, the lift pump may remain off and then may only be powered on when needed. For example, U.S. Pat. No. 7,640,916 describes an approach where under low engine loads, the lift pump remains off, and is only powered on to refill an accumulator.
However, the inventors herein have recognized potential issues with such systems. As one example, when powering on the lift pump during the low fuel flow mode, the lift pump voltage is typically stepped up from 0V to a maximum voltage of the lift pump. Such step changes in the lift pump voltage may result in undesirable in-rush currents which can damage the electrical circuitry of the vehicle as well as cause excessive electromagnetic interference. Further, in port fuel injection (PFI) systems stepping up the electrical power supplied to the lift pump may cause pressure spikes in the fuel line which may result in fuel metering errors during injection.
As one example, the at least some of the issues described above may be at least partly addressed by a method comprising limiting a lift pump voltage to a lower first level when powering on a lift pump from off, maintaining the lift pump voltage at the first level for a duration, and increasing the lift pump voltage above the first level. By limiting the lift pump voltage to the lower first level when powering on the lift pump, in-rush currents may be reduced, resulting in increased longevity of vehicle electrical components. Further, by maintaining the lift pump voltage at the first level for a duration, fuel pressure upstream of a check valve positioned between the lift pump and a fuel rail may be gradually raised to the current fuel rail pressure before fuel rail pressure is increased as desired, reducing pressure spikes in the fuel rail.
In another example, a method for an engine comprises in a first mode, maintaining a lift pump on and adjusting an amount of electrical power supplied to the lift pump based on a difference between a measured fuel rail pressure and a desired fuel rail pressure, and in a second mode, intermittently powering on the lift pump, where powering on the lift pump in the second mode comprises first increasing the amount of electrical power supplied to the lift pump from zero to a lower level, the lower level being a voltage less than a maximum voltage limit of the lift pump, and then monotonically increasing the electrical power supplied to the lift pump to a higher level.
In yet another example, a fuel system comprises a fuel rail, a lift pump positioned upstream of the fuel rail and in fluidic communication with the fuel rail for providing fuel thereto, and a controller in electrical communication with the lift pump, the controller including computer readable instructions stored in non-transitory memory for: providing continuous power to the lift pump when an engine speed is greater than a threshold, and intermittently powering the lift pump in response to the engine speed decreasing below the threshold, where intermittently powering the lift pump comprises stepping up a voltage supplied to the lift pump from zero to a first level when powering on the lift pump from off, and then ramping up the voltage above the first level.
In this way, fuel efficiency may be increased by intermittently powering a lift pump when demands on the lift pump are less than a threshold. Further, in-rush currents and pressure spikes in the fuel rail may be reduced by limiting lift pump voltage when initially powering on the lift pump. As such, electrical component longevity and fuel metering accuracy may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.